FHWA Webinar: Load Rating of Gusset Plates in Steel Truss Bridges by Other States

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FHWA Webinar: Load Rating of Gusset Plates in Steel Truss Bridges by


Other States


Presented By: Anwar S. Ahmad, P.E.


Assistant State Bridge Engineer

Date: October 8, 2009

2

Presentation Outline


About VDOT



Chain of Events Since the I
-
35W Bridge collapse in Minnesota



VDOT’s Approach to Load Rating Gusset Plates

3

About VDOT


VDOT maintains the 3rd largest state
-
owned road system in the U.S.



57,867 miles of sate maintained roadway system



20,918 Structures (Bridges and Large Culverts)

-
19,390 Maintained by VDOT

-
1,528 Maintained by Localities



9 Districts and one Central Office




4

Chain of Events Since the I
-
35W Bridge collapse in Minnesota



Worked with FHWA to identify all bridges with similar design type to
the I
-
35W Bridge (Deck Truss Type)


Total of 11 bridges were identified



Both FHWA and VDOT reviewed the latest inspection reports of the 11
bridges and did not find anything out of the ordinary


All bridges were inspected within the last 2 years of the review date


Some were inspected as early as May 2007



Assigned the inspections of all 11 bridges to the 3 engineering
consulting firms


Inspection completed September 30, 2007

5

Chain of Events Since the I
-
35W Bridge collapse in Minnesota


Identified all FCM bridges and reviewed the last inspection reports (305
total)



Re
-
inspected 36 of the 305 FCM structures for QA measures



Restricted permit vehicles from crossing truss bridges



Identified 113 truss bridges with gusset plates



Developed standard procedure for analyzing gusset plates in
accordance with FHWA latest guidelines



Completed the load rating for 106 of the 113 truss bridges








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Chain of Events Since the I
-
35W Bridge collapse in Minnesota

7

Chain of Events Since the I
-
35W Bridge collapse in Minnesota

8

Chain of Events Since the I
-
35W Bridge collapse in Minnesota

9

VDOT’s Approach to Load Rating Gusset Plates


VDOT decided to follow FHWA
-

LFR Guidelines



VDOT decided to develop examples in MathCAD



Analyze up to 5 members at a joint



Analyze gusset plates and member ends



Separate MathCAD sheet for splice plate


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Typical Connection

VDOT’s Approach to Load Rating Gusset Plates

11



MathCAD Calculations for Gusset Plates at Member Ends


Tension & Compression Check


Fastener Capacity


Block Shear Capacity


Tension / Compression Capacity (Whitmore Section)

VDOT’s Approach to Load Rating Gusset Plates

12



Tension and Compression Checks for Gusset
Plate at Member Ends

VDOT’s Approach to Load Rating Gusset Plates

13



VDOT’s Approach to Load Rating Gusset Plates

MathCAD Sample Calculations

14

VDOT’s Approach to Load Rating Gusset Plates

MathCAD Sample Calculations

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1 = Inventory Rating

2= Operating Rating

VDOT’s Approach to Load Rating Gusset Plates

MathCAD Sample Calculations

16



MathCAD Calculations for Members


Fastener Capacity Check


Block Shear Capacity Check

VDOT’s Approach to Load Rating Gusset Plates

17




MathCAD Calculations For Gusset Plates at Sections
A
-
A, B
-
B and C
-
C


Unsupported Length to Thickness Ratio


Gross and Net Section Shear Yielding Resistance

VDOT’s Approach to Load Rating Gusset Plates

18

Typical Connection

VDOT’s Approach to Load Rating Gusset Plates

19



VDOT’s Approach to Load Rating Gusset Plates

MathCAD Sample Calculations

20



VDOT’s Approach to Load Rating Gusset Plates

MathCAD Sample Calculations

21





Gusset Plate Rating Summary


At each member

VDOT’s Approach to Load Rating Gusset Plates

22




Truss Member Rating Summary


At each member

VDOT’s Approach to Load Rating Gusset Plates

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Final Summary


Controlling Gusset Plate


Controlling Truss Member

VDOT’s Approach to Load Rating Gusset Plates

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VDOT’s Approach to Load Rating Gusset Plates

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VDOT’s Approach to Load Rating Gusset Plates

Example of Gusset Plate Analysis can be found at the following weblink

http://www.virginiadot.org/business/bridge
-
FRP.asp


Thank you!


FHWA Webinar: Load Rating of Gusset Plates in Steel Truss Bridges by


Other States


Presented By: Anwar S. Ahmad, P.E.


Assistant State Bridge Engineer

Date: October 8, 2009